user
Categorize the following items into two different categories and provide a justification for each categorization.

Now complete the following instance -
Input: Stairs, ladder
Output:
assistant
The first item, stairs, can be categorized as a "vertical transportation system", as it is used for going up or down the stairs. The second item, ladder, can be categorized as a "horizontal transportation system", as it is used to get to higher places than the ground.